Colorectal cancer (CRC) is strongly associated with inflammation accompanied by increased infiltration of leukocytes. CCR2, a seven transmembrane G-protein coupled chemokine receptor, mediates several biological functions including chemotaxis of leukocytes upon binding to its ligand, CCL2 (MCP1). CCR2 is expressed on peripheral blood monocytes/macrophages as well as on activated T-cells, B-cells, immature dendritic cells and mast cells. Elevated expression of CCL2 in tumor cells is very well correlated with increased metastasis and poor prognosis in several types of human cancers. Recently, it was shown in animal models that CCL2-CCR2 axis play an important role in promotion of colon tumorigenesis. Our preliminary data showed that CCR2-/- mice in the ApcMin/+ (a spontaneous intestinal cancer mouse model) background developed significantly fewer and smaller size small intestinal and colon tumors and showed substantial survival advantage compared to ApcMin/+ mice. Further, polyps in CCR2-/-ApcMin/+ displayed decreased tumor infiltrating F4/80+ cells, decreased inflammatory molecules (e.g., IL-1?, SOCS1), increased apoptosis and CD8 levels compared to ApcMin/+ mice. Interestingly, inflammatory cytokines IL-23 and IL-17 were significantly reduced in CCR2-/-ApcMin/+. Our gut microbiota analysis revealed that tumor promoting Bacteroides genus are significantly reduced in CCR2-/-ApcMin/+ mice compared to ApcMin/+ mice. Based on these preliminary data we hypothesize that CCR2/CCL2 mediated recruitment of tumor associated macrophages (TAMs) and Th17 cells modulate inflammation and microbiota in the tumor microenvironment to promote intestinal tumors and blocking CCR2-CCL2 axis would reduce the tumor burden. To test this hypothesis we propose two specific aims. In AIM 1 we will determine the requirement of CCR2 for recruitment and activation of IL-23 (TAMs, DCs) and IL-17 (Th17, ?? T-cells) producing cells during intestinal tumorigenesis. In AIM 2, we will determine the influence of gut microflora on CCR2 dependent production of IL-23 and IL-17 to promote intestinal tumorigenesis. The current proposal will also examine the efficacy of existing CCR2 inhibitors in colon cancer progression to translate our basic observation in pre-clinical models. Determining the molecular, cellular mechanisms and complex inter-relationship between immune system-microbiota in the context of cancer will have a strong impact on our basic understanding of intestinal carcinogenesis as well as potential for developing novel therapeutic strategies.